1. Field of the Invention
The present invention relates to a thermal printer, and particularly, to a thermal printer, which can print high-quality images by conveying recording media with high accuracy.
2. Description of the Related Art
A thermal printer 31 in the related art will be described on the basis of JP-A-2002-144616. As shown in FIG. 3, the thermal printer 31 is provided with a printer main body 31a and a cassette mounting part 31b capable of mounting a ribbon cassette 39, to be described below, in the printer main body 31a. 
In addition, a rotatable platen roller 32 is disposed in the printer main body 31a, and a thermal head 33 is disposed above the platen roller 32.
Furthermore, a recording paper 34 is fed between the thermal head 33 and the platen roller 32 so as to be conveyed in a direction of arrow A. The recording paper 34 is made of thick papers such as printing papers, on which color printing can be performed.
Thermal head 33 is supported by a head mounting platen 35, and the head mounting platen 35 is mounted on a head lever.
The head lever is formed in a cantilevered shape, and one end thereof (right side of the drawing) is supported by a supporting shaft 37. The head lever can rotate around the supporting shaft 37 as a fulcrum by a motor acting as a driving source, thereby a free end of the thermal head 33 is attachable to and detachable from (head up/down) the platen roller 32.
In addition, when a ribbon cassette 39, to be described below, is mounted on the cassette mounting part 31b in a head-up state of the thermal head 33, an ink ribbon 38 is positioned between the platen roller 32 and the thermal head 33.
The width of the ink ribbon 38 is larger than that of the recording paper 34 so as to be accommodated in the ribbon cassette 39. Both ends of the ink ribbon 38 are wound on a feed reel 39a and a take-up reel 39b, and the feed reel 39a and the take-up reel 39b are rotatably supported by side plates 39c of the ribbon cassette 39, which face each other.
When the ribbon cassette 39 is mounted on the cassette mounting part 31b, the take-up reel 39b is engaged with a take-up core (not shown) on the printer main body side so as to rotate in the counter-clockwise direction.
As the take-up reel 39b is rotated in the counter-clockwise direction by rotating the take-up core, the ink ribbon 38 wound on the feed reel 39a can be wound on the take-up reel 39b. 
The ribbon cassette 39 is provided with a relief groove 39d for relieving a pressure-contact roller 41, to be described below, and a take-up hole 39e formed at the lower portion of the relief groove 39d. A guide roller 39f made of a metal rod is rotatably supported by the side plate 39c in the vicinity of the take-up hole 39e. 
The ink ribbon 38 is detached from a right end of the head mounting platen 35 at a predetermined detachment angle and bent at about right angle at a guide roller 39f so as to be wound on the take-up reel 39b. 
On the left side of the platen roller 32, the fed roller 40 and the pressure-contact roller 41, which is pressure-contacted with the fed roller 40, are disposed. The recording paper 34 is inserted between the fed roller 40 and the pressure-contact roller 41 and conveyed in the direction of arrow A by rotating the fed roller 40 in the counter-clockwise direction.
When the ribbon cassette 39 is mounted on the cassette mounting part 31b, the pressure-contact roller 41 is positioned in the relief groove 39d. 
The head mounting platen 35 is integrally formed with a guide member (not shown), and the recording paper 34 made of thick paper, which is fed between the thermal head 33 and the platen roller 32 during printing, is bent at a predetermined abutting angle α to the platen roller 32 by the guide member.
However, in the thermal printer 31 in the related art, since the head lever is formed in a cantilevered shape, when the thermal head pressure-contacts the recording paper 34 made of thick paper, and the guide member keeps bending the recording paper 34 until the abutting angle reaches α, the head lever needs sufficient load to rotate.
For this reason, a motor for turning the head lever 36 should be large, which induces the increase in power consumption.
On the other hand, when a motor is small, even when the guide member (not shown), which is integrally formed with the head mounting platen 35, pressure-contacts the recording paper 34 to the platen roller 32 so as to bend the recording paper 34 at the abutting angle α, the recording paper 34 made of thick paper is prone to return to the original shape due to the resilient force of the recording paper 34. Therefore, the thermal head 33 in a head-down state can not reliably pressure-contact the recording paper 34 to the platen roller 32, and high quality image printing cannot be achieved.